Our invention pertains to a turbodrill, or a turbine-operated rotary tool used principally in drilling oil or gas wells, and to certain improved features therein.
Turbodrills in general consist of two basic components: (1) a turbine; (2) a lower bearing; and connected to a drill bit. All but the drill bit of these components are enclosed in what is essentially a single tubular housing. The turbine is mud operated. The mud is pumped into the turbine. The turbine has stators on the housing and rotors on a rotor shaft. The stators function to divert the mud flow onto the rotors, causing the latter to rotate with the rotor shaft and hence with the drill bit connected thereto via a hollow, elongate drive shaft. After actuating the turbine the mud flows through the hollow in the drive shaft and emerges from the drill bit to remove the cuttings out of the drill hole and to cool the bit.
In the turbodrill of the above general configuration it has been known to provide a lubricant chamber just above the lower bearing supporting the drive shaft. The lubricant chamber contains a lubricant, usually oil, for lubricating the lower bearing. The top of the lubricant chamber is bounded by an annular floating piston slidably mounted between drive shaft and housing. The floating piston also forms the bottom of a mud chamber into which there is directed part of the mud that has been used for actuating the turbine. The pressure of the mud in the mud chamber acts on the floating piston to pressurize the lubricant in the lubricant chamber.
A problem with the prior art is that the mud pressure in the mud chamber is considerably more than the mud pressure in the annulus, or the drill hole around the turbodrill. This pressure differential constantly acts, via the floating piston, the lubricant in the lubricant chamber, and the lower bearing, on a seal or seals around the drive shaft which are positioned below the lower bearing to bound the lower end of the lubricant chamber. Consequently the seal or seals under the lower bearing have had to be of highly pressure-proof, costly design for withstanding the pressure differential between mud chamber and annulus.
Another fault of the noted prior art arises by reason of the fact that the mud contains, of course, abrasive sands and other solids. Such abrasive particles deposit on the floating piston, resulting in a rapid failure of the seal or seals between piston and drive shaft.